1. Field of the Invention
The present invention relates to an equipment and a method for annealing semiconductors, in particular, silicon (Si), germanium (Ge), gallium arsenide (GaAs) and so forth.
2. Description of the Prior Art
At present, annealing is drawing the attention of the semiconductor industry in two aspects. One is for the restoration of semiconductor crystals from damages which are caused, for example, by the ion implantation of boron into a silicon wafer by use of high energy with a view to enhancing the performance of a semiconductor element and providing it with a novel function. The most common traditional way of annealing is what is called the electric furnace method, in which the wafer is heated in a furnace, for instance, at 1000.degree. C. for 30 minutes while supplying thereinto dry nitrogen. This method is simple, but it has such defects as follows:
(a) it causes warps in the wafer, thus affecting the productive yield in the ensuing processes;
(b) as heating requires a prolonged time, the interior of the wafer is subject to changes in the ion distribution;
(c) the surface of the wafer is apt to be contaminated; and
(d) prolonged time is needed for annealing. In view of these defects, alternatives therefor are now being sought, e.g., by the application of laser rays for brief exposure of the subject thereto. Laser annealing, however, such as in the case of using a pulse-oscillation laser, also has defects:
(e) the distribution of the implanted ions is subject to substantial changes as their diffusion rate is extremely high in the liquid phase, and the crystal restoration is effected because of the fusion of the wafer surface and the achievement of its crystallization through the liquid epitaxial growth; and
(f) because the radiated light is of a single wavelength, an interference pattern occurs in the melting area, leading to uneven irradiation on the wafer. In the case of employing a continuous oscillation laser,
(g) it means the scanning of a small beam spot on the wafer and thus has defects such as producing a portion wanting sufficient annealing in the linear boundaries between scanning lines, and if the space between the scanning lines is reduced, the scanning takes a prolonged time and often yields overheated portions, thus causing such a disadvantage as uneven irradiation; and
(h) because of the laser light being of a single wavelength an interference pattern is developed on the wafer surface to cause uneven irradiation. A common defect of all of the laser ray annealing methods is the fact they call for large and precise equipments and further advanced techniques for operation.
Another annealing method is for producing, for instance, a silicon wafer by the epitaxial growth of a silicon layer which is deposited on a suitable substrate by means of an ion evaporation technique. The annealing, in such a case, too, was hitherto performed in the same manner as above mentioned, that is, in an electric furnace, or by exposing the wafer to the laser ray, and had the same defects as previously mentioned.